Problem

Swagger UI can't show OpenAPI specs from services running inside the Docker network.

Solution

30 lines for Nginx: https://gitlab.com/plgrnd/swagger-ui/-/blob/main/embedding.conf

Usage

 swagger-ui:
   image: swagger-ui:latest
   environment:
     URLS: '[{"url":"/service-a:8000/v3/api-docs", "name":"service-a"},{"url":"/service-b:9000/v3/api-docs", "name":"service-b"}]'
   ports:
     - "8080:8080"

Result

Start the services and open http://localhost:8080 in your browser. The Servers drop-down will now include option Proxied server url.